Key to the Kingdoms
by toofine89
Summary: Sora and Kairi travel to the House to find the root of Heartless and Nobodies. They must fight new trustees of a kind and their relationship grows. This one shot introduces the story. Each floor will have its own story.


**Let's be blunt. This is after Kingdom Hearts II. I don't care that I twist the story. That is why it is called fanfiction. Anyway, this is a massive crossover to several anime I enjoy, using Kingdom Hearts and The Keys to the Kingdom series as a staging point. I own nothing and never will. The reason this is rated M is possible language, possible explicit material (namely lemons), and violence that will occur.**

**Spoiler Alert to show all cross overs: I'll also reveal the planned floors (as you'll read about later) are Naruto, Bleach, Fairy Tail, Katekyo Hitman Reborn, D. Gray Man, and Claymore. Some worlds will be more canon than others.**

**The Key**

A long time ago, the House was sealed away from all races in the secondary realms. It was known as a sacred place, not to be disturbed, and, over the ages, was sought after. Wars were fought, powerful organizations reigned in terror, and men that could only be described as demons searched after the Ultimate power. Overtime, the truth was lost. Only a descendant of the architect, Arthur, could hold the key that would open the door.

It had been two years since Sora and Riku had returned, and they had all grown to be as close as before, if not closer. Riku had finally taken notice of Selphie who, being only a year younger, was starting to take an interest in him as well. Sora and Kairi, as everyone had always known they would, began seeing each other as soon as Sora returned. Donald and Goofy had traveled back to Disney Castle with the King. After all, both had high ranking positions and had taken several years leave for their adventure. Sora and Riku had caught up with their class and had just graduated this last year. It was the summer before the rest of their lives would start.

The boys, wanting to get the old trio together again, were waiting at "Riku's Island," the small one by the shack that he had claimed for himself long ago, for Kairi. They were sitting, eyes closed, sun on their faces and wind in their hair. A brown mess flowed around Sora's face and liquid silver tossed around Riku's. Sora's outfit was much the same, though he had resorted to wearing just the black tee that was once his bottom layer instead of his jacket. Riku had gone casual and wore time-worn jeans with holes in the knees and a black tee that showed off his muscles. It was almost as if the pants showed the earthy and solid attitude he maintained while the tight shirt showed the darkness barely kept at bay. They heard footsteps coming and they turned around to see Kairi approaching. Her crimson hair streamed behind her and Sora's breath caught in his throat.

Sora really loved her. Her smile that she reserved only for him. Her twilit eyes. Her soft hair that reminded him of ocean waves. Her bell-like laugh that pierced the room and his heart. Her overall cheer, the feeling of warm water in the summer. Her outfit, still pink like it was in The World that Never Was, now hugged the curves of her hips and bosom. And, not to mention, she had developed in the past two years.

In fact, they all had. Riku, Sora, and Kairi had trained ever since they came back. They had destroyed the Organization and Maleficent's army of heartless, but there were still outbreaks, Maleficent's minor mischief, and new threats to worry about. Riku had grown layered muscle, Sora had built up his core and focused on toned muscle like a runner, and Kairi focused on her magic. After all, if something happened to a Princess of Heart, Mickey said something drastic may occur. No, Kairi was best as a support fighter.

It was then he noted what might be worry on her pretty features. She reached them and leaned forward, her hands on her knees, panting from her sprint.

"You okay?" Sora asked her. She looked up and handed Sora a letter she held in her hand.

"Pluto gave it to me," she said, slowly standing up while still breathing heavily.

Sora took it from her hand and turned it over. Pluto usually only delivered messages from the King that were important. The King's seal, a black cartoon resembling King Micky's head, was on the seal and Sora opened it. With Riku looking over one shoulder and Kairi over the other, he read the contents of the cream letter. Odd how something so small could hold a mystery so large.

"Mom! Dad! I've got to go!" Riku was exasperated at this point. "The King has called us to meet him and, as a key bearer, I need to go."

Riku's parents knew about his adventures. In fact, they had known the first day Riku had come back from beating Xemnas. They supported him, but wanted his safety.

His mother and father, standing together with arms crossed stared him down. He crossed his arms and glared back. His father gently put his hand on his mother's shoulder. "He's eighteen. And we know we can trust him. This really seems important to him, dear. Let him go."

Riku's mother burst out in tears and rushed to her son. She gripped him in a back breaking hug, almost as if fearing she would never see him again. She fondly rubbed his back like she used to when he, as a young boy, would come to her for troubles and tears. "I can't believe you're already grown up." She sniffed and held him at arm length, examining him. "Just come back."

Now he held her and comforted her, their roles reversing for the first time. "I will mom. I wouldn't leave my family or these islands for the world, but I'm leaving for all the worlds." He hugged her tight and kissed her on the cheek before moving to his dad. "I guess this is goodbye."

"I guess so," the silver haired giant before him replied. His dad hugged him tightly, let go and ruffled his hair like he did when Riku was young. "Kick ass."

Riku smiled, running out the door with a small pack slung over his back and traveled to the Islands where his friends were waiting. He rowed the boat to the beach with a serious thought teasing the edge of his mind. But, no. It must have just been the darkness that had left him and wanted him back.

He pulled up to the dock and hurriedly tied the boat off, running towards the shack. Behind him, in the ebbs and waves of water, his boat untied due to the rushed job and drifted away from the others, fading off into the distance.

Sora and Kairi sat on the floor of the shack, Sora's head in Kairi's lap, and they sat in a comfortable silence, content in each other's company. The door swung open and Riku stood at the door, smile on his face. Sora smiled too, both looking forward to the adventure. He stood up and brushed himself off, offering Kairi a hand to help her up. She took it and rose to her feet.

Sora's parents had been lost in the heartless attack on Destiny Islands. He had a hard time living without them, but he knew that finding them and releasing them from being heartless, as they likely were, was the biggest favor he could do them. Kairi still lived with her "grandmother" as she called the old woman. In reality, Kairi's parents were unknown. Sora had moved in with Kairi and payed a little rent for a room. It had been easy to get permission to leave for them, but they knew Riku's parents were protective of their only child. "How did you manage to get free?" asked Sora. Blunt as always.

"I don't know. Mom cried and told me to come back safe. Dad said to kick ass. I plan to do both," he said, crossing his huge arms and giving a toothy smile. Sora and Kairi laughed at imagining Riku's dad, usually so serious, saying something so out of character. "Let's go," said the silver haired boy, casting forward an arm as a vortex of dancing black and purple opened in the wall of the shack.

"Last one there buys the seasalt ice-cream!" Sora shouted as he dove through, Kairi in tow. Riku stepped one foot inside the vortex, took one look back to the shack, and entered fully. The portal collapsed with a slight hiss.

Everyone had gathered at the castle that never was and, in silence, climbed to the very top. At the Altar of Naught, they stared at Kingdom Hearts. It had reformed itself since its destruction and, as before, looked like a strange heart-shaped moon, reigning over the strange city that lay barren and busy below.

"Okay, everybody, we're going to get started," stated the King. "I'll explain as much as I can, but it's going to sound weird. Everything that we've ever seen, all the worlds we've been to, were created by one man. He lived in a strange and magical castle along with millions of servants, of whom many were his creations. It is said that he ruled his castle with a series of keys but, due to their power, broke them so that only the strong of heart could use them. They became keyblades. We currently hold all the keys between the six of us, but when we touch them all together, they will combine and only one person should be left with a keyblade, one with the power to open that castle. The way to prevent heartless and Nobodies from forming is said to be in that castle. Any questions?"

Sora's hand was lazily raised up. "What do you mean six? There's only four of us."

"No," was Riku's simple statement. "Can't you feel Roxas and Namine? They are the reason you and Kairi can wield two keyblades at once. My question is, why are we here?"

Mickey nodded sagely at Riku's first comment and then said, "The castle, it seems, is Kingdom Hearts. The only way to open it correctly is to use the merged keyblade and open it without lust or envy for what's inside. That's why it would have been horrific if Xemnas or 'Ansem' had opened it."

Kairi was feeling a little cheated. She just now found out she could use two keyblades, and she was going to have both taken away? Well, at least she'd always have Sora. Not even Kingdom Hearts could take him away from her. Could it? She held him tight at the thought and he squeezed her hand in his as well. He would not forget the promises they had made.

"Okay, then, let's all bring out our keyblades." They did so, smiling at Mickey's Kingdom Key, opposite of Sora's old blade. Way to the Dawn fit snugly in Riku's hand. Sora held Oathkeeper and Oblivion, his clash showing the conflict of light and dark. Kairi held Destiny's Embrace in her right hand and a golden red counterpart to it in her left. The name seemed to come to her. It was Destiny's Maker. Mickey held his keyblade towards the others, and the other bearers touched the tip of his blade with theirs. The insignia so common on Heartless appeared on the ground and leaked a white light that then started to freely flow. They were soon covered so that they could not see each other. In fact, the light was so intense that they could barely see their outstretched arm.

The light soon condensed. The light of Mickey's blade and dark of Riku's flowed into Sora's own blades and they merged into something new. Something powerful. The light became blinding and they all shut their eyes as a sonic shock wave shook the very ground they stood on. When their eyes opened, Sora stood next to Kairi and Riku next to Mickey. Sora held in his hands something beautiful. It was his ultimate weapon, a long broadsword-like keyblade of molten light. It had a gilded gold guard around a simple grip and the blade it self was cut in the shape of a crown, much like they Kingdom Key, however it was not the same. This was pure. This radiated strength and light, though a strong power of darkness came from the black onyx engraved in a swirl down the length of the blade. It seemed to glow and pulse and everyone knew it had no real name. No name could describe what it contained.

Everyone stared wide eyed at the new blade until Mickey turned his eyes away and noticed something odd. Kairi also had keyblades. They were similar to the ones she had before, though they too radiated the purest light. "How do you have key..." he trailed off and looked at Sora now. "You didn't. Did you?"

"What?" asked the clueless brunet as he hugged his girl.

"The only way that she would still have a blade is if she was part of you. Mind, body, and soul."

"Well..." they said, smiling at each other before holding up hands with matching rings. "The diamond rings symbolize body," Sora said.

"The orichalcum rings symbolize mind," said Kairi.

"And they bring us together, so there's the soul. When we got married, just a few weeks ago now, we said that as long as we have these rings, we would stay together. And, after all, a diamond is forever," Sora explained, the love in his eyes clear for Kairi.

"Yep, that's what they said," remarked Riku. He had been one of the two witnesses, the couple's landlady the other. The rest of the island had soon learned.

The King was shocked. "Why didn't I know about this?"

They all gave him a deadpan look. "Our only way to travel to other worlds is my dark corridors. These two can't stand them, they drain me, and Disney Castle can't be accessed by them. It was kind of hard to do," spoke Riku.

"True," the King said with a thoughtful look. "But a marriage is only in name and, like you said, those rings are symbolic. You would've had to have..." he trailed off, realizing the truth.

"Yes, we did. And it went all night long." Sora smiled.

Kairi punched him. "I've never felt so damn sore!" she shouted at him.

"True, but you were still yelling for more," he said, smiling wider as she blushed and the other two felt out of place. They stood in silence, not knowing how to respond, until Mickey changed the subject.

"You'll have to go with Sora, then. Riku, you still have the power of darkness to go home with, and I need to go back to the castle. Sora, Kairi, congratulations. And be careful."

Riku nodded his approval and gave his 'too cool for school' look before heading off. Mickey went the other way and both were surprised when they felt a pull. They suddenly found themselves in the middle of magnet with the newlyweds pulling them into a tight goodbye hug. After nearly being broken into by the hug, they were let go to get their breath back. "And now you can go," said Kairi, a smile playing on her face while Sora laughed at the two who were still gasping for air. They hurried off, afraid of another hug, and Sora and Kairi faced each other.

"Ready love?" asked Sora, his hand under Kairi's chin.

"Just lead the way," Kairi said back to him, and they faced Kingdom Hearts. The Key came to Sora's hand and he pointed it at the door. However, it did not open. They were, instead, pulled inside the very doors. It wasn't unpleasant, but rather disconcerting. Somewhat like traveling through the dark corridors. Except for, all of a sudden, it was not dark. It was bright white, all around. It seemed to be a room, a cube shaped room of pure white and no lighting fixtures, for none were needed. They looked around and saw nothing until they heard something small.

"Ahem," came the sound. There was now a table of white with a white cloth and three white chairs. In one sat a woman who was wearing a white kimono that made her scarlet hair pop even more, much as her golden red eyes popped against her pale skin. And if they were not distinguishing enough, the slight whisker marks, red furred ears, and nine tails definitely gave an odd vibe. She had a white china cup raised to her lips, apparently filled with tea. "Would you care to take a seat, master?"

Sora and Kairi were cautious, but could sense no ill will. They walked over to the table and sat down, hand in hand. "Where are we?" spoke Sora. "Also, if you don't mind, who are you and why are you calling me master?"

"I don't mind at all. We are in the door to the House, though I believe the secondary realms call it Kingdom Hearts. I am Kyuubi, the guardian of the door. And you, master, are my master because of the Key you hold in your heart and in your blood."

Well that just brought up more questions. "House? The keyblade makes me your master? And what's in my blood."

The redheaded beauty leaned back and sighed. This explanation would take some time. "Well, I'm certain you've been to several of the secondary realms. You may call them worlds or planets or something like that, right? They were spawned from Nothing and given shape by the Architect, a creator of all of us except for beings from secondary realms. They developed independently and fascinated the Architect. He created the House to study these realms and set overseers over each part being watched over. He gave each of these people power, but only little control and they used this raw power against him. They took over the House, the second time it has happened, mind you, and sealed him away into that key. If you can wield his pure form, that key, then yes, you are my master and theirs as well, though they will probably not listen to you if didn't to him. Also, only a descendant of his could wield the key so it is in your blood."

Sora's head was spinning and Kairi's was too. Well, if she was a princess, Kairi thought, then by all means he must be a prince if his ancestor made it all. Sora, on the other hand, was just trying to pull it all together. Apparently he was more important than anyone had ever thought. However, it didn't really matter to him if he was important or not, as long as they could stop Nobodies and Heartless from forming in the "secondary realms."

"So, do you mind if I ask you something else?" he asked cautiously.

"Of course you can! How could I refuse my master?" she responded.

"First, could you not call me master? Sora's my name and I'm fine with being called that. Secondly, I didn't come here for these people or this House. I came to find how to stop Heartless and I was told a castle - maybe that's the House, I don't know - had the secret. Heartless are dark creatures, formed from hearts consumed by darkness. Do they sound familiar?"

Kyuubi was thoughtful for a moment, pursing her lips, "Why they sound exactly like Nithlings. Black creatures of varying intelligence, formed from pure Nothing. Each floor of the House is separate and has it's own term for these beings but that is what they truly are. And yes, there is a way to stop them, I suppose. On the top floor is a man who calls himself an Earl. He makes Nithlings and controls Nothing itself. If you were to talk to him, maybe he could stop it. But you'd have to climb each floor along the way, and that may take some time."

"How long?' asked Kairi.

"A couple of decades here, maybe, though that would only be a couple of weeks in your world. Not that it matters. With his key and your connection, you're already immortal. Or at least close to it. You are what we'd call advanced Denizens. You won't age past what you don't want to age past, basic wounds will heal quickly and only extremes like a Nothing bath will kill you. If you keep using those keys, you'll become even stronger."

Sora looked at Kairi. His gaze meant to ask her if it was okay. After all, they may have all the time in the world if Kyuubi was right, but their friends did not. He wanted to help them, but wanted Kairi's approval to spend decades away from these people they knew and loved.

She turned to stare into his eyes. Her eyes held warmth and love. And both uncertainty and faith. She was sad they wouldn't see their friends for a long time, but she also knew that Sora was the only one she needed and that they would make new friends. She squeezed his hand and they both smiled warmly. Sora looked back to Kyuubi while Kairi studied her brunet boy's features. She appreciated how he was strong, but not reeking of masculinity. He was also beautiful, but not feminine. Just what she liked.

"So how do we 'climb' these floors?" asked Sora, determination in his voice.

Kyuubi smiled, knowing Sora was accepting his destiny. "Well, I can start you on the lowest floor through a boy who is connected to me. He is a key, and there is another person who is a lock, as there is on every level. The locks are people who usurped the last Architect, and the keys have strength that can be awakened by your key to help you manage each floor while there and keep it in check while you are gone. If you open each lock by defeating them, either in combat or agreement, the next floor will be opened. I can't tell you who all the locks and keys are, for I only know of this key and of two locks. The key's name is Naruto, and he may grow to be strong. His lock is a vile man named Madara who dreams to take the strength of myself and several powerful Neonithlings - Nithlings that have gained a consciousness and morality of sorts - to make himself indestructible on his floor." She shuddered slightly and a single tear ran down her face in worry for herself, her key, and her master.

Sora felt a strange obligation to help this woman. "Kyuubi, I won't let that happen. I will protect you with this blade." He held it up to emphasize, and the woman smiled. She reached out and touched it.

It sparked in light and eight more keys formed, each identical red. They each had a blood red guard that featured a tail with a handle with eight other tails surrounding it in a slightly asymmetrical fashion. The golden red shafts were about average length and had ridges and teeth that resembled those of some powerful beast. There was, where bright red and dark red collided, a symbol resembling a leaf. It was an emerald, set into the metal. Sora merely thought, and the blades surrounded the table, three around Kairi, three around Kyuubi, and three around himself. Each protecting a precious person. Sora had also changed, growing fox ears, tails, and whiskers. They disappeared in a blinding red light, as did the keys, Sora looking slightly drained.

"Sora," asked Kairi, "is that a drive form?"

"Feels like it," he said to her and, to Kyuubi, "thank you for your strength."

She smiled a foxy smile. "I believe you are also familiar with summoning? The next floor uses that commonly. If you impress me, you may be able to see and summon my true form."

"What's that?" asked Kairi.

Kyuubi gave off a new aura. A base aura, very dangerous. "It feels my key is being attacked and that I may make myself known. Prepare yourself to be transported. It may be a bit jarring." She stood.

"Wait, Kyuubi, who is the other lock you know of?" asked Sora.

"He is the most powerful usurper and an evil man. He is the one I told you about that shapes Nothing and makes Nithlings. His name is the Millennium Earl and he leads several advanced Denizens. Beware his false smile." She started performing hand signs, too many to count, and stopped all of a sudden, roaring in a feral voice. The area was surrounded in fighting shades of red light. The key bearers looked around for where she was, but Sora only caught sight of a beast that would put Cerberus to shame before the light faded and they appeared on a structure covered in mist.

A barrage of needles flew at them and Sora called out, "Reflega!" Each flew back towards the thrower and a gasp of pain was heard. Tired of the blinding mist, Kairi used magnet to gather the mist in one spot. A bridge was revealed along with several people.

Two girls and two boys were covered in needles, immobile and bleeding. Both the girls of rose and ebony hair seemed past saving. The boy with hair like the midnight sky also seemed a hopeless case. A blond boy, however, was healing. Two men, still eyeing each other cautiously, stared at the newcomers. Kairi ran towards the fallen teens and shouted, "Curaga!" with worry evident in her voice. She instantly seemed a tad drained, but the wounds on the boy and black haired girl healed instantly and the needles left their skin.

Still being defensive, worried about the man who could hold thundara in his hand and the man with a sword that Cloud would appreciate, Sora covered himself and Kairi with aerora before speaking. "Who is Naruto and how can I speak to him."

The gray haired man appeared to argue with himself before he spoke. "The blonde you saved with your healing jutsu is Naruto. I am his teacher and protector. The black haired girl and this man are his enemies. The other two are his teammates and the man hiding behind the building supplies," he said while pointing, "is the man my students and I are supposed to protect. However, you see, this man with the meat cleaver is trying to kill us and our client and I am too worn out from trying to save my students to finish him off."

Now that Sora looked closely, he saw the man was swaying on his feet, trying to maintain balance. Zabuza suddenly charged, taking advantage of Kakashi's conversation. However, in a flash, Sora appeared in front of him and blocked his downward strike with two hands behind his Key.

"I am sorry," spoke the key bearer, "but you give the same feel as a Nobody. You do not respect life, it seems, and I must protect Naruto. Please leave with your ally or you will be struck down."

Zabuza looked into the strange boy's blue eyes and saw something odd. It was pure and powerful. It also held no innocence or conceit. He saw the eyes of perfect judgement and had to face his guilt in these eyes, the doorway to this boy's heart. He took his sword and placed it on his back. "Thank you," said the giant of a man. He walked to his student's body, picked her up bridal style, and made a sign with on hand. Mist swirled around him and he was gone.

Sora now looked into the gray haired man's eyes, one dark and one a curious red pattern. "I believe I have not introduced myself to you yet. I am sorry for the deaths of your two students, but if curaga did not help, nothing will except maybe an elixir, something I do not have with me. My name is Sora and my wife's name," he said as Kairi came near, Naruto in her arms, "is Kairi." He placed an arm on her shoulder and she smiled a small smile.

"We are here to help Naruto and hopefully receive his help," she said. She looked at the innocent blonde's face in a near motherly fashion. "Your his teacher, right?"

"Yes," said the man who had released the thundara and sat down, panting. "My name is Kakashi."

"And you have failed," came a deep voice from the side of the bridge that attached to land. There stood a man in a business suit, leaning on a cane. An army of men stood behind him, each armed with various weapons. "We will kill the bridge builder and destroy his creation."

"Shit," swore Kakashi. He was weakened and there were many enemies.

"Do these men value life?" asked Sora.

"No," answered Kakashi while Gato laughed.

"They value money," said the black market man.

"I am sorry then," said Sora. "I hope your hearts will be purer than your actions." He rose his Key in the air and said, in a cold voice filled with regret for destroying life, "Thundaga." An intense display of cold lighting fell from the sky, frying each of Gato's men and Gato himself.

"Well, fuck," said Kakashi before he fainted from chakra exhaustion.

**Anyways, review and share with friends. Criticism is okay and advice is loved. Hate mail is not desirable. Finally I guess I should say I own nothing.**


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